U.S. patent number 5,351,696 [Application Number 08/052,359] was granted by the patent office on 1994-10-04 for method and apparatus for intracardiac electrogram morphologic analysis.
This patent grant is currently assigned to Medtronic, Inc.. Invention is credited to Michael J. German, Ray S. McDonald, Kenneth M. Riff.
United States Patent |
5,351,696 |
Riff , et al. |
October 4, 1994 |
Method and apparatus for intracardiac electrogram morphologic
analysis
Abstract
A method and apparatus for morphologic analysis of an electrical
signal, implementable in an implantable device such as a pacemaker,
cardioverter, defibrillator or the like. The morphologic analysis
uses a phase plane representation of the signal, where the signal
and its first derivative are plotted along orthogonal axes. A
magnitude signal corresponding to the magnitude component of the
trajectory of the phase plane representation is generated and
applied to a comparator. The comparator produces an activation
signal when the magnitude signal exceeds a predetermined threshold.
In response to the activation signal, a quadrant detector
selectively applies the magnitude signal to one of four
integrators, the selection of one integrator over the others being
based at all times upon which quadrant of the phase plane the
trajectory is in. When the magnitude decreases below a
predetermined threshold, the activation signal is deasserted,
whereupon the respective outputs from the four integrators may be
interpreted as reflecting of the trajectory of the phase plane
representation of the signal. In operation, a particular cardiac
event to be detected is induced in a patient, and the resultant
phase plane signals are examined to determine particular aspects of
the phase plane signals which can be used as an indication that the
particular event has occurred. The apparatus is then conditioned to
recognize such aspects in subsequent phase plane signals, in order
to provide an indication when such aspects are again present in the
signals.
Inventors: |
Riff; Kenneth M. (Plymouth,
MN), McDonald; Ray S. (Roseville, MN), German; Michael
J. (Mounds View, MN) |
Assignee: |
Medtronic, Inc. (Minneapolis,
MN)
|
Family
ID: |
21977102 |
Appl.
No.: |
08/052,359 |
Filed: |
April 23, 1993 |
Current U.S.
Class: |
600/515 |
Current CPC
Class: |
A61N
1/371 (20130101) |
Current International
Class: |
A61N
1/362 (20060101); A61N 1/37 (20060101); A61N
1/39 (20060101); A61B 005/0452 () |
Field of
Search: |
;607/9
;128/702-705,695-696 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Ravelli et al, "Proceedings of Computers in Cardiology" Jeruslem,
Israel, Sep. 19-27, 1989, pp. 502-504. .
"Identification of Ventricular Tachycardia Using Intracavitary
Ventricular Electrograms: Analysis of Time and Frequency Domain
Patterns" by Lin et al. in Nov. 1988, Part 1, PACE, vol. 11. .
"Atrial Electrogram Analysis: Antegrade Versus Retrograde", by
McAlister et al., in Nov. 1988 Part II, vol. 11 PACE. .
"Discrimination of Antegrade from Retrograde Atrial Electrograms
for Physiologic Pacing", by Timmis et al., in PACE, vol. 11, Feb.,
1988. .
"Discrimination of Antegrade and Retrograde Atrial Depolarization
by Electrogram Analysis", by Pannizzo, et al., in American Heart
Journal, Oct., 1986. .
"Detection of Pathological Tachycardia by Analysis of Electrogram
Morphology", by Davis, et al., in PACE, vol. 9, Mar.-Apr., 1986.
.
"Ideal Atrial Lead Positioning to Detect Retrograde Atrial
Depolarizationn by Digitization and Slope Analysis of the Atrial
Electrogram", by Wainwright, et al., in PACE, vol. 7, Nov.-Dec.,
1984, Part II..
|
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Duthler; Reed A. Patton; Harold
R.
Claims
What is claimed is:
1. A method of identifying a cardiac event as being of a specific
type, comprising the steps of:
monitoring a patient's EGM signal during a cardiac event;
generating a four quadrant phase plane trajectory representation of
said patient's EGM signal during said event:
defining a metric reflecting the relative areas circumscribed by
said phase plane trajectory in each said quadrant; and
identifying said event as being of said specific type in response
to said phase plane trajectory corresponding to said metric;
wherein said generating step comprises:
applying said patient's EGM signal to a filter circuit and to a
differentiator circuit to produce a filtered EGM signal and a
differentiated EGM signal;
applying said filtered EGM signal to a squaring circuit to produce
a filtered, squared signal;
applying said differentiated EGM signal to a squaring circuit to
produce a squared, differentiated EGM signal;
summing said squared, differentiated EGM signal and said filtered,
squared EGM signal to produce a summation signal;
applying said summation signal to a square root circuit to produce
a magnitude signal corresponding to a magnitude component of said
phase plane trajectory representation of said patient's EGM
signal;
defining said four quadrants of said phase plane trajectory
representation;
for each said quadrant, separately integrating said magnitude
signal to produce a separate integration signal for each said
quadrant; and
wherein said identifying step comprises indicating occurrence of an
event of said specific type when said integration signals correlate
in accordance with said metric.
2. A method for indicating occurrences of a specific type of
cardiac event comprising the steps of defining at least one
characteristic feature of a patient's EGM signal when said specific
type of event occurs and thereafter detecting said at least one
characteristic feature of said patient's EGM signal;
wherein said step of defining said at least one characteristic
feature comprises
defining a metric expressing a correlation of four areas
circumscribed by a four quadrant phase plane trajectory;
and wherein said step of detecting said at least one characteristic
feature comprises the sub-steps of:
monitoring said patient's EGM signal during a cardiac event;
generating a phase plane representation of said EGM signal, said
phase plane representation comprising trajectory in a phase plane
having four quadrants, said generating step in turn comprising
deriving, from said patient's EGM signal, four integration signals,
each one of said four integration signals reflecting an area
circumscribed by said phase plane trajectory in one said quadrant
of said phase plane representation of said EGM signal; and
indicating an occurrence of an event of said specific type when
said four integration signals correlate in accordance with said
metric.
3. An apparatus for detecting occurrences of a specific type of
cardiac event, comprising:
a magnitude signal generating circuit means, responsive to an EGM
signal from a patient's heart for generating a magnitude signal
corresponding to a phase plane trajectory representation of said
EGM signal, said phase plane trajectory representation
corresponding to a plot of said EGM signal versus a first
derivative of said EGM signal in a phase plane having four
quadrants;
first, second, third, and fourth integrator circuits, each
associated with a different one of said four phase plane quadrants,
each coupled to said magnitude generating circuit, each integrator
circuits comprising means for producing an integration signal
corresponding to an area circumscribed by said phase plane
trajectory in its associated quadrant of said phase plane;
a discriminating circuit, coupled to said first, second, third, and
fourth integrator circuits and comprising means responsive to
receipt of first, second, third, and fourth integration signals
having a predetermined correlation for producing produce an event
detected signal indicative of occurrence of a cardiac event of said
specific type, wherein said predetermined correlation is
predetermined based upon analysis of an said patient's EGM signal
during an induced occurrence of said specific event.
4. A method of identifying a cardiac event, comprising the steps
of:
applying a patient's EGM signal to an amplifier circuit and to a
differentiator circuit to produce an amplified EGM signal and a
differentiated EGM signal;
applying said amplified EGM signal to a squaring circuit to produce
a squared, amplified EGM signal;
applying said differentiated EGM signal to a squaring circuit to
produce a squared, differentiated EGM signal;
summing said squared, differentiated EGM signal and said squared,
amplified EGM signal to produce a summation signal;
applying said summation signal to a square root circuit to produce
a magnitude signal;
separately integrating said magnitude signal (a) while said
differentiated EGM signal is positive and said amplified EGM signal
is positive, (b) while said differentiated EGM signal is negative
and said amplified EGM signal is positive, (c) while said
differentiated EGM signal is positive and said amplified EGM signal
is negative, and (d) while said differentiated EGM signal is
negative and said amplified EGM signal is negative, to produce four
separate integration signals; and
identifying said event as a function of relative magnitudes of said
integration signals.
5. A method of identifying a cardiac event, comprising the steps
of:
applying a patient's EGM signal to an amplifier circuit and to a
differentiator circuit to produce an amplified EGM signal and a
differentiated EGM signal;
combining said amplified EGM signal and said differentiated EGM
signal to produce a magnitude signal;
separately integrating said magnitude signal (a) while said
differentiated EGM signal is positive and said amplified EGM signal
is positive, (b) while said differentiated EGM signal is negative
and said amplified EGM signal is positive, (c) while said
differentiated EGM signal is positive and said amplified EGM signal
is negative, and (d) while said differentiated EGM signal is
negative and said amplified EGM signal is negative, to produce four
separate integration signals; and
identifying said event as a function of relative magnitudes of said
integration signals.
6. A method of identifying a cardiac event, comprising the steps
of: applying a patient's EGM signal to an amplifier circuit and to
a differentiator circuit to produce an amplified EGM signal and a
differentiated EGM signal;
applying said amplified EGM signal to a squaring circuit to produce
a squared, amplified EGM signal;
applying said differentiated EGM signal to a squaring circuit to
produce a squared, differentiated EGM signal;
summing said squared, differentiated EGM signal and said squared,
amplified EGM signal to produce a summation signal;
applying said summation signal to a square root circuit to produce
a magnitude signal;
separately integrating said magnitude signal while said
differentiated EGM signal meets a first predefined criterion and
said amplified EGM meets a second predefined criterion to produce
an integration signal; and
identifying said event as a function of magnitude of said
integration signal.
7. A method of identifying a cardiac event, comprising the steps
of:
applying a patient's EGM signal to an amplifier circuit and to a
differentiator circuit to produce an amplified EGM signal and a
differentiated EGM signal;
combining said amplified EGM signal and said differentiated EGM
signal to produce a magnitude signal;
separately integrating said magnitude signal while said
differentiated EGM signal meets a first predefined criterion and
said amplified EGM signal meets a second predefined criterion to
produce an integration signal; and
identifying said event as a function of magnitude of said
integration signal.
8. Apparatus for identifying a cardiac event, comprising:
means for sensing a patient's EGM signal;
amplifier means, coupled to said sensing means, for producing an
amplified EGM signal;
differentiator means, coupled to said sensing means, for producing
a differentiated EGM signal;
first squaring means, coupled to said filter means, for producing a
filtered, squared signal;
second squaring means, coupled to said differentiator means, for
producing a squared, differentiated EGM signal;
summing means, coupled to said first and second squaring means, for
summing said squared, differentiated EGM signal and said filtered,
squared EGM signal to produce a summation signal;
square root determining means, coupled to said summing means, for
producing a magnitude signal;
means for separately integrating said magnitude signal (a) while
said differentiated EGM signal is positive and said amplified EGM
signal is positive, (b) while said differentiated EGM signal is
negative and said amplified EGM signal is positive, (c) while said
differentiated EGM signal is positive and said amplified EGM signal
is negative, and (d) while said differentiated EGM signal is
negative and said amplified EGM signal is negative, to produce four
separate integration signals; and
means for identifying said event as a function of relative
magnitudes of said integration signals.
9. Apparatus for identifying a cardiac event, comprising:
means for sensing a patient's EGM signal;
amplifier means, coupled to said sensing means, for producing an
amplified EGM signal;
differentiator means, coupled to said sensing means, for producing
a differentiated EGM signal;
means for combining said amplified and differentiated EGM signals
to produce a magnitude signal;
means for separately integrating said magnitude signal (a) while
said differentiated EGM signal is positive and said amplified EGM
signal is positive, (b) while said differentiated EGM signal is
negative and said amplified EGM signal is positive, (c) while said
differentiated EGM signal is positive and said amplified EGM signal
is negative, and (d) while said differentiated EGM signal is
negative and said amplified EGM signal is negative, to produce four
separate integration signals; and
means for identifying said event as a function of relative
magnitudes of said integration signals.
10. Apparatus for identifying a cardiac event, comprising:
means for sensing a patient's EGM signal;
amplifier means, coupled to said sensing means, for producing an
amplified EGM signal;
differentiator means, coupled to said sensing means, for producing
a differentiated EGM signal;
first squaring means, coupled to said filter means, for producing a
filtered, squared signal;
second squaring means, coupled to said differentiator means, for
producing a squared, differentiated EGM signal;
summing means, coupled to said first and second squaring means, for
summing said squared, differentiated EGM signal and said filtered,
squared EGM signal to produce a summation signal;
square root determining means, coupled to said summing means, for
producing a magnitude signal;
means for separately integrating said magnitude signal while said
differentiated EGM signal meets a first predefined criterion and
said amplified EGM signal meets a second predefined criterion to
produce an integration signal; and
means for identifying said event as a function of magnitude of said
integration signal.
11. Apparatus for identifying a cardiac event, comprising:
means for sensing a patient's EGM signal;
amplifier means, coupled to said sensing means, for producing an
amplified EGM signal;
differentiator means, coupled to said sensing means, for producing
a differentiated EGM signal;
means for combining said amplified and differentiated EGM signals
to produce a magnitude signal;
means for separately integrating said magnitude signal while said
differentiated EGM signal meets a first predefined criterion and
said amplified EGM signal meets a second predefined criterion to
produce an integration signal; and
means for identifying said event as a function of magnitude of said
integration signal.
Description
FIELD OF THE INVENTION
This invention relates generally to the field of medical devices,
and more particularly relates to an implantable medical device
having circuitry for analyzing the morphology of intracardiac
electrogram signals.
BACKGROUND OF THE INVENTION
Among the various types of devices for monitoring and/or
therapeutically stimulating a patient's heart, a great many are
known which are responsive to detected cardiac activity to operate
in a particular manner. Perhaps the most common example of such a
device is the so-called demand pacemaker, which is responsive to
sensed electrical cardiac activity in either or both chambers of
the heart, such that pacing pulses are delivered only in the
absence of intrinsic cardiac activity. Implantable, cardiac
defibrillators and cardioverters are also typically made responsive
to sensed electrical cardiac activity.
For any device in which proper operation depends upon sensing and
interpreting cardiac electrogram (EGM) signals, it is of course
desirable to enable the device to accurately interpret the signals
and to correctly identify the various types of electrical events,
including atrial beats (P-waves), ventricular beats (QRS
complexes), and so on, which may occur. For example, it is common
in demand pacemakers for various timing intervals to be started or
stopped based upon detection of ventricular activity. Thus, a
sensed ventricular event might inhibit a ventricular pacing output
and initiate a base rate timer, a V-A escape interval timer, and an
upper rate limit timer, while a sensed atrial event might inhibit
an atrial pacing output and initiate an A-V delay interval timer.
Operation of the pacemaker then depends upon whether certain
expected events occur, and, if so, when such events occur in
relation to the various time intervals established by the
pacemaker.
While certain types of EGM events may be quite readily detected
with a fair degree of certainty, there are certain other types of
EGM events which are susceptible to being misinterpreted,
misidentified (i.e., a false positive indication), or undetected
(i.e., a false negative indication). As manifested in an EGM
signal, viewed, for example, on a cathode ray tube or paper strip
chart, one event may have only very subtle morphological
differences from another, making discrimination and identification
of either of the events quite difficult. The misidentification of,
or inability to detect specific types of EGM events can have such
undesirable consequences as preventing a therapeutic device from
properly treating the heart, or improperly allowing the device to
deliver a therapy when none is actually needed.
The ability to distinguish different morphologies would be useful
in a number different situations, such as when it is necessary to
discriminate between normal (antegrade) and abnormal (retrograde)
activation of the atria. Such ability would be useful in preventing
pacemaker mediated tachycardia (PMT), in which retrograde P waves
or far-field R-waves cause continuous A-V sequential pacing at a
high rate. At the present time, PMT is typically prevented by
programming a prolonged post-ventricular atrial refractory period
(PVARP) so that the retrograde P wave or far-field R-wave is not
"seen" by the atrial channel; however, this limits the upper
tracking rate of the pacemaker. Alternatively, various algorithms
have been developed to terminate PMT once it is established. The
ability to distinguish antegrade from retrograde P waves or
far-field R-waves would be a far better solution to the problem of
PMT. In this situation, retrograde P waves or far-field R-waves
would be ignored by the pacemaker, abolishing the potential for
PMT.
Another situation in which the ability to distinguish between the
subtly different morphologies of certain types of EGM events is
when it is necessary to discriminate between normal ventricular
activation and abnormal ventricular activation. This would be
useful in premature ventricular contraction (PVC) detection as well
as detection of ventricular arrhythmias, such as ventricular
tachycardia. Current generations of defibrillators use only a rate
criteria to distinguish between normal beats and arrhythmias; the
ability to distinguish between normal and abnormal EGM morphologies
would be a significant improvement.
Various methods have been proposed in the prior art for
distinguishing between different electrogram morphologies. In
Wainwright et. al., "Ideal Atrial Lead Positioning to Detect
Retrograde Atrial Depolarization by Digitization and Slope Analysis
of the Atrial Electrogram ", PACE, 7:1152-1158, (1984), for
example, there is proposed a digital system for examining changes
in slew rates of the atrial EGM signals recorded from the right
atrial appendage, high right atrium, and low right atrium, in order
to distinguish antegrade from retrograde P waves. However, the
signal processing capabilities described by Wainwright appear to be
beyond that currently available in implantable devices.
Davies et. al., "Detection of Pathological Tachycardia by Analysis
of Electrogram Morphology", PACE, 9:200-208, (1986), discussed the
possibility of using the method described by Wainwright et al. to
distinguish normal from abnormal ventricular activation. In Panizzo
et. al., "Discrimination of Antegrade and Retrograde Atrial
Depolarization by Electrogram Analysis", American Heart Journal,
112:780-786 (1986), measurement of EGM amplitudes and slew rates
was proposed to distinguish antegrade from retrograde atrial
activation. Panizzo et al. apparently concluded that combining a
magnitude and slew rate threshold allowed discrimination of
antegrade from retrograde P waves in 34 of 34 cases examined.
Timmis et. al., "Discrimination of Antegrade from Retrograde Atrial
Electrograms for Physiologic Pacing", PACE, 11:130-140 (1988)
discussed the examination of multiple EGM parameters, including
peak-to-peak amplitude, duration, energy, maximum slew rate, mean
slew rate, and polarity in the time domain, and maximum frequency,
half-power frequency, Fourier amplitude peak, and frequency of peak
in the frequency domain, and apparently concluded that no single
parameter reliably distinguished antegrade from retrograde atrial
activation, although the use of multiple parameters could be
useful.
McAlister et. al., "Atrial Electrogram Analysis: Antegrade Versus
Retrograde", PACE, 11: 1703-1707 (1988) suggested examination of
morphology, slew rate, and amplitude criteria in discriminating
antegrade from retrograde P waves, and seemed to indicate that
morphology and slew rate did not increase the discriminatory power
over amplitude alone. Lin et. al., "Identification of Ventricular
Tachycardia Using Intracavitary Ventricular Electrograms: Analysis
of Time and Frequency Domain Patterns", PACE, 11:1592-1606 proposed
the use of sophisticated signal processing techniques, including
correlation analysis and spectral analysis, in distinguishing
ventricular tachycardia from sinus tachycardia, and suggested that
the correlation waveform analysis is a reliable technique which
requires significant data processing resources.
In view of the foregoing, it appears to the inventor that it would
be desirable to provide morphologic analysis capability in an
implantable device, in order to improve the device's ability to
accurately detect and respond to various classes of EGM events.
SUMMARY OF THE INVENTION
The present invention relates to a method of distinguishing between
EGM morphologies using phase space analysis. The phase space is an
N-dimensional space with a variable x(t) plotted along one axis and
N-1 of its derivatives, (dx(t)/dt, d.sup.2 x(t)/dt.sup.2, etc.)
plotted along mutually orthogonal axes. As x(t) and its derivatives
vary in time, the point corresponding to the instantaneous values
of x(t) and its derivatives can be plotted in phase space.
Therefore, as the signal x(t) evolves in time, a curve (known as
trajectory) is traced in phase space with time as a parameter. In
the two-dimensional case where the relevant variables are x(t) and
its first derivative dx(t)/dt, the phase space becomes a phase
plane.
The advantage of phase space representations of a time-varying
signal is that each of the axes (i.e., the signal and its
derivatives) yields additional information about the signal; i.e.,
it is a way of increasing knowledge about what the signal is doing.
Phase space representations can facilitate the observer's ability
to detect subtle shifts in morphology of the signal, since both the
signal as well as its derivatives are being examined for changes.
In addition, periodic behavior is readily distinguished from
non-periodic behavior by examining the patterns of the trajectories
in phase space. As would be appreciated by those of ordinary skill
in mathematics, the relevant measurements in the phase plane
consist of: the magnitude, herein referred to as r(t), (i.e.,
distance of the point from the origin) of the trajectory at each
point in time; and the angle, herein .alpha.(t), of the trajectory
at each point in time.
Once the trajectory has been constructed and its magnitude and
phase angle plots have been made, it is then possible to define a
metric, i.e., a set of criteria, that can be applied in order to
distinguish between the different trajectories of different
signals. There are an infinite number of potential metrics than can
be defined; some potential ones that could be derived by relatively
simple hardware (i.e., hardware which could be included in an
implantable device) include: determination of maximum value of the
magnitude plot, determination of the angle of the trajectory at the
maximum value of the magnitude, measurement of the area under the
magnitude curve, measurement of the area under the phase angle
curve, determination of the value of the largest derivative of the
magnitude plot, or determination of the value of the largest
derivative of the phase angle plot.
It is to be noted, however, in accordance with an important aspect
of the present invention, that phase plane analysis is primarily a
conceptual tool. Any practical realization of this method would not
actually plot phase plane trajectories, but would use the concept
in the design of the hardware or software to distinguish different
signals.
In order to develop the concept of phase plane analysis of EGM
signals, actual human atrial electrograms were obtained in a
digitized format from a computer database. EGMs were obtained from
two patients, LB and MM. Normal antegrade P waves were recorded for
each patient. Retrograde P waves, caused by pacing the ventricle in
the presence of retrograde (VA) conduction, were recorded for each
patient. The signals analyzed were bipolar EGMs. The morphologies
of the antegrade and retrograde P waves were quite different for
patient MM and quite similar for patient LB, allowing a fair
analysis of the technique.
Based upon these experimental results, the inventor has determined
that there are numerous ways to distinguish antegrade from
retrograde atrial EGM signals using phase plane representations.
Possible metrics include: the number of complete circles around the
origin while the magnitude exceeds a certain threshold, the angle
of the maximum magnitude vector, or the mean value of the angle
while the magnitude exceeds a certain threshold.
In accordance with one feature of the present invention, therefore,
an apparatus is provided for analyzing EGM signals in the phase
plane, and to generate signals representative of certain features
of the phase plane representation of the EGM signals. In accordance
with another feature of the present invention, the phase plane
analysis circuitry is relatively simple, such that it may be
readily implemented in an implantable device, such as a pacemaker,
cardioverter, or defibrillator.
Another feature of the present invention is that the circuitry can
be readily adapted to provide an indication of different
characteristics of an EGM signal's trajectory in the phase plane,
including, but not limited to, the number of circles made by the
trajectory around the origin while the magnitude exceeds a
predetermined threshold, the angle of the maximum magnitude vector
of the trajectory, the mean value of the angle while the magnitude
exceeds a predetermined threshold, and the areas under the
magnitude and angle curves.
In accordance with another feature of the present invention, the
information provided by the phase plane analysis circuitry provides
an implantable device with a wide array of data from which specific
types of events may be rendered distinguishable. In a preferred
embodiment of the invention, circuitry is provided for deriving a
plurality of phase plane parameters reflecting certain
characteristics of a phase plane representation of a human EGM
signal. In operation, the apparatus must first be "taught" or
conditioned to recognize a particular event that is to be detected.
This is accomplished by inducing an occurrence of the specified
event in the patient, and applying the patient's EGM signals during
the induced event to apparatus of the present invention. The phase
plane parameters derived by the apparatus in response to the
induced event EGM signals are then used to define a metric to be
used as a basis for detection of future occurrences of the
particular event. That is, various interrelationships among the
phase plane parameters generated in response to the induced event
are identified. Thereafter, when the patient's EGM signals are
applied to the apparatus and such interrelationships are observed
in the resulting phase plane parameters, these parameters can be
taken as an indication that the specified event has occurred.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other aspects of the present invention will be
best appreciated with reference to the detailed description of a
specific embodiment of the invention, which follows, when read in
conjunction with the accompanying drawings, wherein:
FIGS. 1a, 1b, 1c, and 1d are plots of portions of human cardiac
electrogram signals;
FIGS. 2a, 2b, 2c, and 2d are plots of the first derivative of the
EGM signals from FIGS. 1a, 1b, 1c, and 1d, respectively;
FIGS. 3a, 3b 3c, and 3d are phase plane plots derived from the
plots from FIGS. 1a and 2a, and 1b, and 2b, 1c and 2c, and 1d and
2d, respectively;
FIGS. 4a, 4b, 4c, and 4d are magnitude plots derived from the phase
plane plots of FIGS. 3a, 3b, 3c, and 3d, respectively;
FIGS. 5a, 5b, 5c, and 5d are angle plots derived from the phase
plane plots of FIGS. 3a, 3b, 3c, and 3d, respectively;
FIG. 6 is a block diagram of a phase plane analysis apparatus in
accordance with one embodiment of the invention;
FIG. 7 is a sample phase plane trajectory plot;
FIG. 8a is a plot of a sample filtered EGM signal and its
derivative; FIG. 8b is a sample phase plot corresponding to the EGM
signal and derivative from FIG. 8a; and FIG. 8c is a plot of the
output signals produced by integrators in the circuit of FIG. 6 in
response the signals from FIG. 8a;
FIG. 9a is a plot of a sample filtered EGM signal and its
derivative; FIG. 9b is a sample phase plot corresponding to the EGM
signal and derivative from FIG. 9a; and FIG. 9c is a plot of the
output signals produced by integrators in the circuit of FIG. 6 in
response the signals from FIG. 9a;
FIG. 10a is a plot of a sample filtered EGM signal and its
derivative; FIG. 10b is a sample phase plot corresponding to the
EGM signal and derivative from FIG. 10a; and FIG. 10c is a plot of
the output signals produced by integrators in the circuit of FIG. 6
in response the signals from FIG. 10a;
FIG. 11a is a plot of a sample filtered EGM signal and its
derivative; FIG. 11b is a sample phase plot corresponding to the
EGM signal and derivative from FIG. 11a; and FIG. 11c is a plot of
the output signals produced by integrators in the circuit of FIG. 6
in response the signals from FIG. 11a;
FIG. 12 is a schematic diagram of the bandpass filter and amplifier
from the block diagram of FIG. 6;
FIG. 13 is a schematic diagram of the bandpass filter and the
differentiator from the block diagram of FIG. 6;
FIG. 14 is a schematic diagram of the squaring circuits and adder
from the block diagram of FIG. 6;
FIG. 15 is a schematic diagram of the square root circuit and
comparator with hysteresis from the block diagram of FIG. 6;
FIG. 16 is a schematic diagram of the quadrant detector from the
block diagram of FIG. 6;
FIG. 17 is a schematic diagram of the switches and integrators from
the block diagram of FIG. 6;
FIG. 18 is a schematic diagram of the valid data circuit and reset
circuit from the block diagram of FIG. 6; and
FIG. 19 is a schematic diagram of the initial/final sign detector
from the block diagram of FIG. 6.
DETAILED DESCRIPTION OF A SPECIFIC EMBODIMENT OF THE INVENTION
Referring first to FIGS. 1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b, 5a, and
5b, there are shown a series of plots which will facilitate an
understanding of the present invention. In FIGS. 1a and 1b, there
is shown an EGM plot of x.sub.a (t) showing an antegrade atrial
event (P-wave) within the dashed line designated as 10 and an EGM
plot of x.sub.r (t) showing a retrograde P-wave within the dashed
line designated as 12, respectively, from the aforementioned
experimental subject MM. FIGS. 2a and 2b are plots of the
respective first derivatives with respect to time, i.e., dx.sub.a
(t)/dt and dx.sub.r (t)/dt, of the curves x.sub.a (t) and x.sub.r
(t) shown in FIGS. 1a and 1b. Next, in FIGS. 3a and 3b, there are
shown phase plane plots of the signals from FIGS. 1a and 1b,
respectively; that is, the phase plane plot of FIG. 3a corresponds
to the graph of x.sub.a (t) from FIG. 1a (on the horizontal axis)
versus dx.sub.a (t)/dt from FIG. 2a (on the vertical axis), while
the phase plane plot of FIG. 3b corresponds to the graph of x.sub.r
(t) from FIG. 1b versus dx.sub.r (t)/dt from FIG. 2b. FIGS. 4a and
4b are plots of the respective magnitude functions r.sub.a (t) and
r.sub.r (t) versus time, where the magnitude function r.sub.a (t)
corresponding to curves of FIGS. 1a and 2a is calculated as
##EQU1## and the magnitude function r.sub.r (t) corresponding to
the curves of FIGS. 1b and 2b is similarly calculated as ##EQU2##
Finally, FIGS. 5a and 5b are plots of the respective angle
functions .alpha..sub.a (t) and .alpha..sub.r (t) versus time,
where .alpha..sub.a (t) is computed as ##EQU3## and .alpha..sub.r
(t) is similarly computed as ##EQU4## where the positive x-axis is
defined as 0.degree. and the angle increases in the
counterclockwise direction. The negative x-axis is 180.degree. and
the angle changes from 359.degree. to 0.degree. as it crosses the
positive x-axis from below.
As shown in FIG. 3a, the phase plane plot of the antegrade P-wave
designated within dashed line 10 starts just left of the origin,
makes one large loops, designated as 13 in FIG. 3a, in the
clockwise direction, returning to a point just left of the origin,
then makes one small clockwise loop, designated as 14 in FIG. 3a.
The angle of the maximum amplitude vector, designated as 15 in FIG.
3a, is 180.degree. . This can also be seen with reference to a
comparison of the plot of magnitude versus time shown in FIG. 4a
with the plot of angle versus time shown in FIG. 5a; that is, when
the magnitude is at a maximum, the angle is at 180.degree. . The
double transition of the angle plot through 360.degree. (one
designated as 16, one designated as 18 in FIG. 5a) signifies two
complete rotations of the trajectory around the origin. It will be
appreciated by those of ordinary skill in the art that the multiple
transitions of the angle plot through 360.degree. designated
generally as 20 in FIG. 5a represent "jitter" of the trajectory of
FIG. 1a back and forth across the x-axis; the very small magnitude
corresponding to these multiple transitions (see the corresponding
area denoted generally as 22 in the magnitude plot of FIG. 4a)
suggests that this is merely "noise" which can be accounted for in
practice through the use of a threshold comparator, as shall be
hereinafter described in greater detail.
Referring now to the phase plane plot of FIG. 3b corresponding to
the retrograde P-wave 12 in the region designated within dashed
line 12, it will be noted that there is only one complete circling
of the origin, designated as 26 in FIG. 3b, as can also be seen as
the single transition 28 through 360.degree. the plot of
.alpha..sub.r (t) in FIG. 5b. Referring to FIGS. 4b and 5b
together, the angle of the maximum magnitude vector 30 in FIG. 3b
is 0.degree. instead of 180.degree. as in the antegrade case. The
angle plot of FIG. 5b has a prolonged initial period at around
0.degree., in contrast to the antegrade case. The phase plane plot
of FIG. 3b also has considerable low-level "jitter" of the angle
around 0.degree., which can be accounted for with a threshold
comparator as noted above.
From a comparison of the plots of FIGS. 1a, 2a, 3a, 4a, and 5a with
FIGS. 1b, 2b, 3b, 4b, and 5b, it will be appreciated by those of
ordinary skill in the art that a number of metrics for
distinguishing between antegrade and retrograde P-waves may be
considered, including the number of complete circles around the
origin while the magnitude vector exceeds a predetermined threshold
value, the angle of the maximum magnitude vector, or the mean value
of the angle while the magnitude vector exceeds a predetermined
threshold value.
In the particular case illustrated in FIGS. 1a-b, 2a-b, 3a-b, 4a-b,
and 5a-b, it is apparent that one way of distinguishing between
antegrade and retrograde P-waves in this patient is to compare the
mean value of the magnitude vector in each quadrant of the phase
plane. This may be accomplished, for example, by integrating the
trajectory function separately for each quadrant of the phase
plane. If the quadrants are identified as quadrant I (r>0;
0.degree.<.alpha.<90.degree.), quadrant II (r>0;
90.degree.<.alpha.<180.degree.), quadrant III (r>0;
180.degree.<.alpha.<270.degree.), and quadrant IV (r>0;
270.degree.<.alpha.<360.degree.), then for this particular
patient, a metric for distinguishing between antegrade and
retrograde P-waves could be expressed as follows: upon detection of
an atrial event, if the integral of phase plane trajectory in
quadrants II and III are greater than those for quadrants I and IV,
this indicates an antegrade P-wave, while if the integral of the
phase plane trajectory in quadrants I and IV are greater than those
for quadrants II and III, this indicates a retrograde P-wave.
Similar data from experimental subject LB is depicted in FIGS.
1c-d, 2-d, 3c-d, 4c-d, and 5c-d. In particular, FIG. 1c is a plot
of an antegrade P-wave (designated within dashed line 10') and FIG.
1d is a plot of a retrograde P-wave (designated within dashed line
12') as reflected in patient LB's EGM signal. FIGS. 2c and 2d are
plots of the first derivative of the signals from FIGS. 1c and 1d,
respectively. FIG. 3c is a plot of the phase plane trajectory
obtained by plotting the function x.sub.a (t) from FIG. 1c against
the function dx.sub.a (t)/dt from FIG. 2c; similarly, FIG. 3d is a
plot of the phase plane trajectory obtained by plotting the
function x.sub.r (t) from FIG. 1d against the function dx.sub.r
(t)/dt from FIG. 2d. FIGS. 4c and 5c are the plots of the magnitude
and angle components, respectively, of the phase plane trajectory
of FIG. 3c, and FIGS. 4d and 5d are the plots of the magnitude and
angle components, respectively, of the phase plane trajectory of
FIG. 3d.
Examination of the respective phase plane trajectories resulting
from antegrade and retrograde P-waves in patient LB suggests that
the metric used for distinguishing between antegrade and retrograde
P-waves in patient MM (described with reference to FIGS. 3a-b
above) would not be appropriate for distinguishing between these
two events in patient LB. Instead, analysis of the trajectories
from FIGS. 3c and 3d shows that the area circumscribed by the
trajectory of FIG. 3c for an antegrade P-wave is nearly one and
one-half times greater than the area circumscribed by the
trajectory of FIG. 3d for a retrograde P-wave. Thus, antegrade and
retrograde P-waves could be distinguished based upon the sum of the
integral of the phase trajectory in all four quadrants of the phase
plane--if this sum exceeds a certain level, this could be taken as
an indication of an antegrade P-wave, while if it does not, this
could be taken as an indication of a retrograde P-wave.
Although the same metric may not be appropriate for detection of a
particular cardiac event in every patient, it is contemplated that
for a given patient, absent such additional complications such as
ischemia or myocardial infarction, a given metric that is found
suitable for a patient based upon observation of an induced event
will continue to be a reliable and consistent indicator of the
event in that patient. Thus, once a suitable metric has been
defined for a patient, it will continue to be effective for that
patient over a relatively long term.
Although a number of possible metrics have been noted herein, the
present invention relates to a generalized, multi-function hardware
arrangement which may generate many different signals and signal
combinations reflecting various different aspects of the signal
morphology. Thus, it is contemplated that the presently disclosed
embodiment of the invention may have diverse applications and may
be readily adapted to perform many different types of morphologic
analyses. The present invention is not intended to be limited to a
particular set of morphologic criteria. Furthermore, it is believed
that different metrics may be more or less suitable for the
purposes of discriminating between different kinds of events; that
is, a metric which proves suitable for distinguishing antegrade
from retrograde P-waves may not be as well-suited for
distinguishing normal from premature ventricular contractions. It
is contemplated, however, that the invention disclosed herein is
suitable for many purposes, including not only atrial event
discrimination and ventricular event discrimination, but also
detecting ventricular tachycardia, ventricular fibrillation, atrial
fibrillation, and so on.
Turning now to FIG. 6, there is shown a block diagram of a
phase-plane analysis circuit in accordance with one embodiment of
the present invention. The circuit represented in FIG. 6 includes a
bandpass filter and amplifier 110 which receives an EGM signal at
its input. The bandpass filtered and amplified EGM signal
(hereinafter referred to as x(t) is then conducted on line 111 to
the respective inputs of a bandpass filter 112 and a differentiator
114. The filtered output signal from bandpass filter 112 is then
applied, via line 113 to a first squaring circuit 116, while the
differentiated output signal from differentiator 114 is conducted
on line 115 to a second squaring circuit 118. Thus, if the signal
on line 113 is denoted x(t), then the signal on line 115 is
dx(t)/dt.
The output from squaring circuit 116, which corresponds to x.sup.2
(t), is applied on line 117 to one input of a summing circuit 120,
while the output from squaring circuit 118, which corresponds to
(dx(t)/dt).sup.2, is applied to a second input of summing circuit
120. The output from summing circuit 120 therefore corresponds to
x.sup.2 (t)+(dx(t)/dt).sup.2, and is applied on line 121 to a
square root circuit 122. The positive output of square root circuit
122 thus corresponds to the magnitude vector r(t), where r(t) is
given by the equation ##EQU5##
The r(t) signal on line 123 is applied to an input of a comparator
with hysteresis 124, and also to an input of a series of integrator
circuits 136, 138, 140, and 142. Comparator with hysteresis
produces an output signal on line 125 which goes high when the
magnitude signal r(t) on line 123 exceeds a predetermined
threshold, and which goes low when r(t) falls to a predetermined
level below the predetermined threshold. This hysteresis function
performed by comparator 124 prevents the output signal from
toggling on and off repeatedly should r(t) assume a value nearly
equal to the predetermined threshold of comparator 124, as would be
appreciated by those of ordinary skill in the art.
The signal on line 125 is applied to an enable input of a quadrant
detector 126, which also receives as inputs the x(t) and dx(t)/dt
signals on lines 113 and 115, respectively. Quadrant detector 126
produces four output signals, on lines 128, 130, 132, and 134. When
quadrant detector 126 is enabled by the signal on line 125 at its
enable input, the signal on line 128 is asserted when both of its
inputs (i.e., x(t) and dx(t)/dt) are positive; i.e., r is in
quadrant one. The signal on line 130, on the other hand, is
asserted when detector 126 is enabled and when x(t) is negative but
dx(t)/dt is positive; i.e., r is in quadrant two. The signal on
line 132 is enabled when detector 126 is enabled, x(t) is negative
and dx(t)/dt is negative; i.e., r is in quadrant three. Finally,
the signal on line 134 is asserted when detector 126 is enabled and
when x(t) is positive and dx(t)/dt is negative; i.e., r is in
quadrant four. Thus, the signals on lines 128, 130, 132, and 134
function to identify which quadrant of the phase plane the phase
plane representation of the EGM signal is currently in, so long as
the representation of the EGM signal currently has a magnitude
vector which exceeds the predetermined threshold set by comparator
with hysteresis 124.
Thus, as will be appreciated by those of ordinary skill in the art,
comparator with hysteresis 124 prevents the circuit of FIG. 6 from
responding to the low-level "jitter" of phase-plane plots
previously described above with reference to FIGS. 5a and 5b.
With continued reference to FIG. 6, the magnitude signal r(t) is
applied to the inputs of the series of selectively actuable
switches 135, 137, 139, and 141. Switches 135, 137, 139, and 141
are normally "open", so that signals at their respective inputs are
not conducted to their respective outputs. However, output signal
lines 128, 130, 132 and 134 from quadrant detector 126 are applied
to ENABLE inputs of respective switches 135, 137, 139, and 141, so
that when one of the quadrant detector outputs is asserted, a
corresponding one of switches 135, 137, 139, and 141 will be
"closed", allowing magnitude signal r(t) on line 123 to be
conducted from the input of that switch through to its output, to
be applied to a respective one of integrators 136, 138, 140 or
142.
At any given time, at most one of the quadrant-identifying signals
will be asserted, so that at any given time, only one of the
integrators 136, 138, 140, or 142 will have the magnitude signal
r(t) applied thereto via a corresponding one of switches 135, 137,
139, and 141. Thus, the output of each integrator 136, 138, 140,
and 142 is a value representing the amount and duration of time
that the magnitude signal r(t) exceeds the predetermined threshold
value of comparator 124 in a particular quadrant and is
proportional to the area within the trajectory in each respective
quadrant.
As shown in FIG. 6, the output signal on line 125 from comparator
124 is, in addition to being applied to the ENABLE input of
quadrant detector 126, also applied to the input of a valid data
indicator circuit 154. Valid data indicator circuit is essentially
a falling-edge triggered one-shot circuit which asserts an output
signal on line 156 when comparator 124 deasserts its output signal
on line 125. The data valid signal on line 156 is provided to
morphology discriminating circuit 152 to indicate completion of a
phase plane trajectory analysis (i.e., to indicate when a
trajectory no longer exceeds the threshold value of comparator
124). In addition, the data valid signal on line 156 is applied to
an input of a reset circuit 158. In response to an assertion of the
data valid signal on line 156, reset circuit 158 waits for a
predetermined time interval and then asserts an output signal on
line 159 which is applied to a RESET input of integrators 136, 138,
140 and 142. The predetermined time interval corresponds to a data
valid window during which time the output voltages from integrators
136, 138, 140 and 142 may be examined by discriminating circuit
152. After this time interval, reset circuit asserts the signal on
line 159, thereby resetting the outputs of integrators 136, 138,
140, and 142 in preparation for analysis of another trajectory
having sufficient magnitude to trigger comparator 124.
The circuit of FIG. 6 also includes a circuit 162 for identifying
the initial and final signs of the derivative. Initial/final sign
detector circuit 162 receives the signal on line 115 corresponding
to dx(t)/dt. In addition, circuit 162 receives the enable signal
conducted on line 125. When the enable signal on line 125 goes
high, indicating that r(t) has exceeded the predetermined threshold
of comparator 124, the initial sign (i.e., positive or negative) of
dx(t)/dt is latched by circuit 162. Similarly, when the signal on
line 125 goes low, the final signal of dx(t)/dt is latched by
circuit 162. Signals representing the initial and final signs of
dx(t)/dt are then conducted on output lines 166 and 167 to
morphology discriminating circuit 152, where they may be
incorporated into the metric for identifying a particular phase
plane trajectory morphology.
Operation of the circuit represented in FIG. 6 will perhaps be
better understood with reference to an example of a phase plane
trajectory 160, shown in FIG. 7. It is to be understood that curve
160 in FIG. 7 is only an example of a phase plane trajectory, and
is substantially simplified, for the purpose of illustration, as
compared with signals derived from actual EGM inputs to the circuit
of FIG. 6.
In FIG. 7, phase plane trajectory 160 begins, at a time t.sub.0, at
a point 162 (t.sub.0) near the origin. As phase plane trajectory
160 travels outward from point 162 beginning at time t.sub.0, its
magnitude component r(t) increases. In FIG. 7, circle 166
represents the threshold of comparator 124, such that any signal
having a magnitude less than that threshold will not cause the
output from comparator 124 to become asserted. When the magnitude
component r(t) of phase plane trajectory 160 is less than the
threshold value of comparator 124, (i.e., when phase plane
trajectory 160 is within circle 166 in FIG. 7), quadrant detector
126 is not enabled, and all switches 135, 137, 139, and 141 are
open. Therefore, in this situation, integrators 136, 138, 140, and
142 integrate a zero value; therefore, the outputs from integrators
136, 138, 140, and 142 would remain unchanged. It is to be
understood that initially, the integrators' output values are all
zero, due to the above-described operation of reset circuit
158.
At a time t.sub.1, the magnitude component r(t) of phase plane
trajectory 160 crosses threshold circuit 166, at a point designated
as 163. At time t.sub.1, therefore, comparator 124 will assert its
output on line 125, thereby enabling quadrant detector 126. Since
both x(t) and dx(t)/dt are positive at time t.sub.1, quadrant
detector 126 will assert the signal on line 128 to close the switch
135 corresponding to positive x(t) and positive dx(t)/dt. As a
result, the magnitude signal r(t) will be conducted to the input of
integrator 136, which will perform an integration of the r(t)
signal. This is reflected in an increase in the output signal from
integrator 136 on line 144 in the interval between times t.sub.1
and t.sub.2.
At point 170 (time t.sub.2), phase plane trajectory 160 crosses the
horizontal axis, with dx(t)/dt now being negative. Since r(t) still
exceeds threshold line 168, quadrant detector 126 remains enabled,
but asserts the signal on line 134 instead of that on line 128,
since dx(t)/dt is now negative. Therefore, at time t.sub.2 switch
141 will be closed and switch 128 will be re-opened. Thus,
integrator 136 resumes integration of a zero value while integrator
142 begins integrating the magnitude signal r(t) in the time
interval between times t.sub.2 and t.sub.3.
At point 172 (time t.sub.3) in FIG. 7, phase plane trajectory 160
crosses the vertical axis, so that both x(t) and dx(t)/dt are now
negative. This causes quadrant detector to assert the signal on
line 132 instead of that on line 130, closing switch 139 and
opening switch 141. Thus, at time t.sub.3 integrator 140 will begin
integrating the magnitude signal r(t) and integrator 142 will cease
doing so.
At point 174 (time t.sub.4) in FIG. 7, trajectory 160 again crosses
the horizontal axis, so that dx(t)/dt is now positive and x(t)
remains negative. Thus, at time t.sub.4, integrator 138 will begin
integrating the magnitude function r(t) applied thereto via switch
137, and integrator 140 will cease doing so.
At point 176 (time t.sub.5) in FIG. 7, trajectory 160 crosses the
vertical axis so that both x(t) and dx(t)/dt are once again both
positive. As before, this will result in application of the
magnitude signal r(t) to integrator 136 via switch 135, resulting
in a second interval of increase in the output from integrator
136.
At some time after time t.sub.5, trajectory 160 turns inward toward
the origin, crossing into circle 166 at point 178, and crossing
into circle 180 at a point 182 (time t.sub.6). Circle 180
represents a second threshold value corresponding to the voltage at
which comparator 124 will deassert its output signal on line 125.
The threshold value represented by circle 180 is less than that
represented by circle 166; this difference arises due to the
hysteresis of comparator 124. As would be appreciated by those of
ordinary skill in the circuit art, the fact that comparator 124 has
a hysteresis function means that although a signal having a
magnitude greater than that represented by circle 166 in FIG. 7 is
required before comparator 124 will assert its output, the signal
must fall below the level represented by circle 180 before
comparator 124 will deassert its output.
At time t.sub.6, when trajectory 160 crosses threshold 180 and
magnitude function r(t) crosses threshold 184, comparator 124 will
deassert its output on line 125, thereby disabling quadrant
detector 126. Thus, none of switches 135, 137, 139, and 141 will be
closed, and the output voltages from integrators 136, 138, 140, and
142 will thereafter remain unchanged.
In addition, when comparator 124 deasserts the output signal on
line 125, data valid detector asserts its output signal on line
156, indicating to discriminating circuit 152 that the output
values from integrators 136, 138, 140 and 142 may be read.
Discriminating circuit 152 must read the integrator output values
during the time window defined by the time delay of reset circuit.
After this time delay, reset circuit will issue its reset signal on
line 159, restoring the output values of integrators 136, 138, 140
and 142 to zero values. Thus, the circuit of FIG. 6 is put into a
state of readiness for a subsequent input signal having a phase
plane trajectory with magnitude sufficient to trigger comparator
124.
As previously noted, the phase plane trajectory of FIG. 7 is a
hypothetical one that has been provided only for the purposes of
describing the operation of the circuit of FIG. 6. In FIGS. 8a-c
through 12a-c, there are shown various plots of actual signals
applied to the circuitry of FIG. 6. As shown in FIG. 6, the EGM
input signal is applied to the EGM input of bandpass filter and
amplifier 110. The output of filter/amplifier 110 is then applied
to the respective inputs of filter 112 and differentiator 114. If
the output of filter 112 is designated as x(t) then the output of
differentiator 114 is dx(t)/dt, the first derivative of x(t). In
FIG. 8a, a first waveform V113 corresponds to the bandpass filtered
EGM signal x(t) that is conducted on line 113 in the circuit of
FIG. 6. A second waveform V115 in FIG. 7a represents the
differentiated EGM signal dx(t)/dt that is conducted on line 115 in
the circuit of FIG. 6.
In FIG. 8b, there is shown a phase-plane plot of the waveforms V113
and V115, with waveform V113 being plotted along the X-axis and
waveform V115 being plotted on the Y-axis. In FIG. 8c, there are
shown the waveforms of the outputs of integrators 136, 138, 140,
and 142, which outputs are conducted on lines 144, 146, 148, and
150, respectively. In FIG. 8c, the signal conducted on line 144 is
designated as V144, the signal on line 146 is designated as V146,
and so on.
As would be appreciated by those of ordinary skill in the art, the
waveform V144 in FIG. 8c represents the amount and duration of time
that the phase plane trajectory of FIG. 8b exceeds the
predetermined threshold value of comparator 124 in quadrant one of
the phase plane, and is proportional to the area within the
trajectory of FIG. 8b in quadrant one. Notice from FIGS. 8b and 8c
that waveform V144 increases during the interval from time t.sub.0
to t.sub.1, while the phase plane trajectory of FIG. 8b is in
quadrant 1. Similarly, waveform V150 represents the amount and
duration of time that the phase plane trajectory of FIG. 8b exceeds
the predetermined threshold value of comparator 124 in quadrant
four of the phase plane, and is proportional to the area within the
trajectory in quadrant four. Thus, waveform V150 increases during
the interval from time t.sub.1 to t.sub.2.
It should be noted that waveforms V146 and V148 in FIG. 8c stay at
a zero value, since the trajectory of FIG. 8b does not enter
quadrants two or three.
FIGS. 9a, 9b, and 9c are, like FIGS. 8a, 8b, and 8c, plots showing
an filtered input signal (V113 in FIG. 9a) that appears on line 113
in the circuit of FIG. 6, its derivative (V115 in FIG. 9a) that
appears on line 115, the phase plane trajectory obtained by
plotting V113 versus V115 (FIG. 9b), and the output waveforms from
integrators 136, 138, 140, and 142 (waveforms V144, V146, V148, and
V150 in FIG. 9c).
Likewise, FIGS. 10a-c and 11a-c are sets of plots showing a
filtered input signal (V113) and its derivative (V115) (FIGS. 10a
and 11a) the corresponding phase plane plot (FIGS. 10b and 11b) and
the integrator output waveforms (V144, V146, V148, and V150) (FIGS.
10c and 11c), for different input EGM signals.
When discriminating circuit reads the integrator output values, it
is thereby provided with information about the morphology of the
incoming EGM signal which would not be apparent from analysis of
the signal alone, without the phase plane analysis which takes into
account the signal and at least one of its derivatives. In
accordance with an important feature of the present invention, it
is contemplated that in addition to the integrator output values,
discriminating circuit may also be provided with other signals that
are produced within the circuit shown in FIG. 6, such as the
magnitude signal r(t) on line 123, the signals x(t) and dx(t)/dt on
lines 113 and 115, respectively, or the incoming EGM signal itself.
It is for the sake of clarity only that connections for directly
providing such additional signals to discriminating circuit 152 are
not shown in FIG. 6.
It is further contemplated that additional derivatives of x(t) may
be produced in the circuit of FIG. 6, by merely cascading
differentiator circuits identical to 114 in FIG. 6 in a manner
which would be readily apparent to one of ordinary skill in the
art. Such additional derivative signals could then be used in more
comprehensive discriminating metrics which might be realized in
discriminating circuit 152.
Also, with regard to the magnitude threshold established by
comparator 124, which threshold has a circular representation in
the phase plane, it is contemplated that variations on this
threshold function could be implemented. For example, comparators
might be interposed along lines 113 and 115 to activate switches
135, 137, 139, and 141 whenever x(t) is within predetermined upper
and lower limits at the same time that dx(t)/dt is within
predetermined upper and lower limits. Such an arrangement would
result in a threshold which would be represented in the phase plane
as a rectangular region, rather than circular one. In any case, it
is believed to be preferable for the threshold to be capable of
being varied so that in a practical application of the invention
the circuit may be customized according to an individual patient's
parameters.
It is further contemplated that simple circuitry that could be
readily provided by those of ordinary skill in the circuit art
might be applied to the output of quadrant detector 126, so that,
for example, the number of complete revolutions of the phase plane
trajectory of a signal might be monitored and counted, such
information also being applied to discriminating circuitry 152 to
be used in conjunction with a particular metric.
Since, as described above, the appropriate metric for identifying a
particular cardiac event may differ from one patient to the next,
an important step in the utilization of an apparatus in accordance
with the present invention is the conditioning of discrimination
circuitry 152 to recognize certain distinguishing features of the
phase plane signals specific to an individual patient. It is
contemplated that such conditioning may be accomplished by first
inducing in the patient the event to be detected in accordance with
the present invention, and then evaluating features and
characteristics of the resultant phase plane trajectory. Having
done so, a metric may be selected that is appropriate for the
patient. Circuitry for allowing programmability or selection of the
metric to be used for a given patient may include RAM or ROM memory
for storing digital representations of analog values against which
the integrator output signals may be compared; or analog reference
voltage storage devices; or hard-wired analog and digital
circuitry.
For example, in the case of experimental subject MM whose
trajectories for antegrade and retrograde P-waves were depicted in
FIGS. 3a and 3b above, it was determined that a comparison of the
integrals from quadrants II and III with those from quadrants I and
IV would served to distinguish antegrade from retrograde P-waves.
It is believed that it would be a matter of routine for those of
ordinary skill in the art to implement a comparison of such values
in discrimination circuitry 152. For example, it would be a simple
matter to apply the integrator signals from integrators 136. 138,
140, and 142 to voltage comparators in order to produce an
ANTEGRADE output signal from circuit 152 when the integrals from
quadrants II and III exceed those from quadrants I and IV, and a
RETROGRADE output signal from circuit 152 when the opposite
relationship exists.
In the case of experimental subject LB whose phase plane
trajectories for antegrade and retrograde P-waves were depicted in
FIGS. 3c and 3d, it would be a matter of routine to sum the outputs
signals from integrators 136, 138, 140, and 142, and to then
produce an ANTEGRADE output signal when this sum exceeds a
predetermined level and a RETROGRADE output signal when this sum
does not exceed a predetermined level.
It is further believed that it would be a matter of routine for
those of ordinary skill in the art to provide general,
multi-function circuitry 152 which would be programmably
controllable to perform various types of comparisons, summations,
or other basic operations on the integrator output signals in order
to generate signals reflecting various features of the phase plane
trajectory, as appropriate for a given patient.
Although the metric appropriate for identifying a particular
cardiac event in one patient may not be appropriate for another, it
is believed that for a given patient, once an appropriate metric
has been defined, it should provide a reliable and consistent basis
for discrimination between different events over a relatively long
period of time, unless a condition that might change the
morphology, such as ischemia, myocardial infarction, or the like
arises.
Turning now to FIGS. 12 through 19, there are shown more detailed
schematic diagrams of the circuitry represented in block form in
FIG. 6. In FIGS. 12 through 19, it is to be understood that
corresponding components in the block diagram of FIG. 6 have
retained identical reference numeral designations. For example, the
specific circuitry embodying bandpass filter and amplifier 110 in
the block diagram of FIG. 6 is similarly designated within a dashed
line 110 in FIG. 12. Also, it is to be understood that a certain
component shown on one of the schematics of FIGS. 12 through 19 may
be connected to a component shown on a different one of those
schematics. For example, bandpass filter 110 in FIG. 12 is coupled,
via conductor 111 to the inputs of bandpass filter 112 and
differentiator 114 shown in FIG. 13. It will be assumed therefore
that conductor 111 in FIG. 12 is connected to and identical to
conductor 111 in FIG. 13.
The types and values of each of the components shown in FIGS. 12
through 19 are set forth in the following Table 1. Each of the
components are commercially available, off-the-shelf pans; it is
contemplated, however, that particularly in the context of an
implantable device, the present invention would advantageously be
practiced with a custom integrated circuit, or the like.
TABLE 1 ______________________________________ Item Quantity
Reference Part ______________________________________ 1 1 C84 1.5
nf 2 2 C1 68 .mu.f C2 68 .mu.f 3 61 C3 0.1 .mu.f C4 0.1 .mu.f C5
0.1 .mu.f C6 0.1 .mu.f C7 0.1 .mu.f C8 0.1 .mu.f C9 0.1 .mu.f C10
0.1 .mu.f C11 0.1 .mu.f C12 0.1 .mu.f C13 0.1 .mu.f C14 0.1 .mu.f
C15 0.1 .mu.f C16 0.1 .mu.f C17 0.1 .mu.f C18 0.1 .mu.f C19 0.1
.mu.f C20 0.1 .mu.f C21 0.1 .mu.f C22 0.1 .mu.f C23 0.1 .mu.f C24
0.1 .mu.f C25 0.1 .mu.f C26 0.1 .mu.f C27 0.1 .mu.f C28 0.1 .mu.f
C29 0.1 .mu.f C30 0.1 .mu.f C31 0.1 .mu.f C32 0.1 .mu.f C33 0.1
.mu.f C34 0.1 .mu.f C35 0.1 .mu.f C36 0.1 .mu.f C37 0.1 .mu.f C38
0.1 .mu.f C39 0.1 .mu.f C40 0.1 .mu.f C41 0.1 .mu.f C42 0.1 .mu.f
C43 0.1 .mu.f C44 0.1 .mu.f C45 0.1 .mu.f C46 0.1 .mu.f C47 0.1
.mu.f C48 0.1 .mu.f C49 0.1 .mu.f C50 0.1 .mu.f C51 0.1 .mu.f C52
0.1 .mu.f C53 0.1 .mu.f C54 0.1 .mu.f C55 0.1 .mu.f C56 0.1 .mu.f
C57 0.1 .mu.f C58 0.1 .mu.f C59 0.1 .mu.f C60 0.1 .mu.f C61 0.1
.mu.f C62 0.1 .mu.f C80 0.1 .mu.f 4 2 C63 0.1 .mu.f C71 0.1 .mu.f 5
1 C64 0.33 .mu.f 6 1 C65 0.38 .mu.f 7 3 C66 3.19 .mu.f C67 3.19
.mu.f C68 3.19 .mu.f 8 1 C69 33 nf 9 1 C70 10 .mu.f 10 1 C72 0.01
.mu.f 11 1 C73 30 pf 12 1 C75 100 .mu.f 13 4 C76 1 .mu.f C77 1
.mu.f C78 1 .mu.f C79 1 .mu.f 14 1 C82 0.01 15 1 C83 22 nf 16 1 D1
1N4148 19 1 R1 100 M.OMEGA. 20 1 R2 1 M.OMEGA. 21 13 R3 10 K.OMEGA.
R6 10 K.OMEGA. R7 10 K.OMEGA. R8 10 K.OMEGA. R17 10 K.OMEGA. R22 10
K.OMEGA. R31 10 K.OMEGA. R40 10 K.OMEGA. R41 10 K.OMEGA. R42 10
K.OMEGA. R43 10 K.OMEGA. R70 10 K.OMEGA. 22 2 R4 500 K.OMEGA. R37
500 K.OMEGA. 23 1 R5 5 K.OMEGA. 24 1 R10 760 K.OMEGA. 25 1 R11 1.03
M.OMEGA. 26 1 R12 208 K.OMEGA. 27 1 R13 8 K.OMEGA. 28 1 R14 24
K.OMEGA. 29 1 R15 318 K.OMEGA. 30 1 R16 640 K.OMEGA. 31 1 R18 115
K.OMEGA. 32 1 R19 7.96 K.OMEGA. 33 1 R20 79.6 K.OMEGA. 34 1 R21 7.5
K.OMEGA. 35 1 R23 9.5 K.OMEGA. 36 1 R24 1.5 M.OMEGA. 37 6 R25 100
K.OMEGA. R26 100 K.OMEGA. R27 100 K.OMEGA. R28 100 K.OMEGA. R36 100
K.OMEGA. R69 100 K.OMEGA. 38 1 R29 2.2 K.OMEGA. 39 1 R30 47
K.OMEGA. 40 4 R32 20 K.OMEGA. R33 20 K.OMEGA. R34 20 K.OMEGA. R39
20 K.OMEGA. 41 2 R35 1 K.OMEGA. R38 1 K.OMEGA. 42 4 R44 56 K.OMEGA.
R45 56 K.OMEGA. R46 56 K.OMEGA. R47 56 K.OMEGA. 43 4 R56 50
K.OMEGA. R57 50 K.OMEGA. R58 50 K.OMEGA. R59 50 K.OMEGA. 44 1 R67
110 k.OMEGA. 45 1 SW1 1RSW10 46 1 U1 LH0036 47 2 U2 LM324 U3 LM324
48 1 U4 LM308 49 3 U5 AD532 U6 AD532 U7 AD532 50 10 U8 LM311 U9
LM311 U10 LM311 U11 LM311 U12 LM311 U13 LM311 U14 LM311 U15 LM311
U16 LM311 U35 LM311 51 4 U17 LF351 U18 LF351 U19 LF351 U20 LF351 52
1 U25 LM2931T 53 5 U26 IH5141 U28 IH5141 U29 IH5141 U30 IH5141 U31
IH5141 54 1 U34 4538 55 1 U36 74HC74 56 1 U37 74HC04
______________________________________
In FIG. 12, there is shown a schematic diagram of one
implementation of bandpass filter and amplifier 110 from the block
diagram of FIG. 6. FIG. 13 shows a schematic diagram of one
implementation of bandpass filter 112 and differentiator 114 from
the block diagram of FIG. 6. FIG. 14 shows squaring circuits 116
and 118, and summing circuit 120 from the block diagram of FIG. 6.
FIG. 15 is a schematic diagram of one implementation of square root
circuit 122, and comparator with hysteresis 124 from the block
diagram of FIG. 6. FIG. 16 shows a schematic diagram of one
implementation of quadrant detector circuit 126 from the block
diagram of FIG. 6. FIG. 17 is a schematic of switches 135, 137,
139, and 141, and integrators 136, 138, 140, and 142 from the block
diagram of FIG. 6, and FIG. 18 shows a schematic diagram of one
implementation of valid data circuit 154 and reset circuit 158 from
the block diagram of FIG. 6. FIG. 19 is a schematic of
initial/final sign detector 162 from the block diagram of FIG.
6.
From the foregoing detailed description of a particular embodiment
of the invention, it should be apparent that a method and apparatus
for conducting phase plane analysis of EGM signals has been
disclosed. It is believed that the presently disclosed invention
may be advantageously implemented within an implantable pacemaker,
cardioverter, defibrillator or the like, in order to enhance the
event-discriminating capability of the implantable device. One
pacemaker in which the present invention may be implemented is that
disclosed in U.S. Pat. No. 5,052,388 to Sivula et al., which patent
is hereby incorporated by reference in its entirety.
Although a specific embodiment of the invention has been described
herein in some detail, this has been done for the purposes of
illustration only, and is not intended to be limiting with respect
to the scope of the present invention. It is contemplated that
various substitutions, alterations, and modifications may be made
to the embodiment of the invention described herein, even if such
substitutions, alterations, or modifications were not specifically
noted herein, without departing from the spirit and scope of the
present invention, as defined in the appended claims which
follow.
* * * * *